President Obama has been, hands down, the least popular figure at Saturday’s Freedom Summit in Iowa—blistered for what Republicans here cast as his unconstitutional overreach, for scandals at the Veterans Affairs Department and the IRS, and for his policies on immigration and abortion rights.

A close second? The unofficial front-runners for the Republican presidential nomination in 2016.

Donald Trump, the showman who perennially threatens to run for president—and who said Saturday that he was pondering 2016 again—searingly criticized both Mitt Romney and Jeb Bush, the leading establishment presences at this exceedingly early stage of the campaign.

“It can’t be Mitt because Mitt ran and failed. You can’t have Romney; he choked,” said Trump, revving the crowd.

But then he went on: “You can’t have Bush. The last thing we need is another Bush.”

Trump blamed Bush’s brother, former President George W. Bush, for being the man who “gave us Obama,” and he criticized the former Florida governor’s support for the Common Core educational standards, as well as his more moderate position on illegal immigration.

“Remember his statement: 'They came for love,'” Trump said as he mocked a past comment by Jeb Bush about undocumented immigrants to the U.S. “Half of them are criminals; they’re coming for love?”

Incendiary as he was, Trump was not the most popular speaker so far at the summit, which was due to stretch until after nightfall at an old restored theater outside downtown Des Moines. That position was held by retired neurosurgeon Ben Carson, a tea party favorite who brought the crowd to its feet, and Wisconsin Gov. Scott Walker.

2016 presidential possibilities

“Do we have an illegal immigration problem?” he asked the crowd.

“Yes!” they shouted in return.

“Can we fix it?”

“Yes!”

Carson, along with other speakers, said the problem was a matter of political will, and he demanded the construction of a wall blocking the entire border.

He said it was necessary to treat immigrants in the country illegally with “compassion," although his solution was to set up a system of work permits that would have to be applied for outside of the United States.

Walker gave a more invigorated presentation than his speech a week ago to Republican National Committee leaders in Coronado, Calif., touting gains he said his state had made during his tenure.

He cited legislation protecting gun owners and pulling back regulations on small businesses and farms. But the crowd roared when he cited two high-profile conservative priorities.